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# Radio Waves and Signals - PowerPoint PPT Presentation

Radio Waves and Signals. Week 4. We imagine radio signals/waves travel as sine waves. The ripple of these waves are started by the vibration of an electron. The signal is produced in the circuits of the r adio, once the vibration leaves the radio through the antenna it becomes

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Presentation Transcript

travel as sine waves.

The ripple of these waves are started by

the vibration of an electron

The signal is produced in the

the vibration leaves the

antennait becomes

Radio waves are just one part

of the electromagnetic spectrum

An electromagnetic wave consists

of a vibrating

electric field

and a

vibrating

magnetic

field.

It is the electromagnetic wave

that carries the radio signal between the

transmitting

and

receiving

stations.

The EM wave oscillates in such a way to

mimic the signal that generated the wave.

A cycle is one complete vibration.

This diagram actually shows 3 cycles.

Wavelength (l) is the distance the wave

travels in 1 complete cycle

The number of vibrations per second

is the frequency.

What is the

frequency of

each wave?

1 second

2 Hz

10 Hz

Frequency is measured in Hertz (Hz):

1 vibration/sec is 1 Hz

AM stations broadcast in kilohertz (kHz)

1330 KVOL broadcasts at 1,330,000 Hz

FM stations broadcasts in megahertz (MHz)

96.5 KPEL broadcasts at 96,500,000 Hz

What type of wave carries radio

signals between transmitting

and receiving stations?

Electromagnetic

What is the name for the distance

1 complete cycle?

Wavelength

What term describes the number of times per second that an alternating current reverses direction.

frequency

In what unit is frequency measured?

Hertz

1

1

A Hertz is ____ vibration(s) per _____ second(s)

What are the two components of a radio wave? (or any other wave in the electromagnetic

spectrum)

Electric and

magnetic fields

All radio waves travel at the speed

of light (c) through a particular type

of medium.

The speed of light through

space is 300,000,000 m/s

Since all radio waves travel at the speed of light no matter what their frequency happens to be the following is true:

When length increases

then frequency decreases

or

when length decreases

then frequency increases.

Radio waves can be referred to by

wavelength or frequency because

the two are related by the speed of light.

c

f

l

A wave with a length of 2 m means

it has a frequency of 150,000,000 Hz

because

300,000,000 / 150,000,000 = 2

This frequency typically would be referred to as 150 MHz

Wavelength in meters = 300 divided by frequency in megahertz.

300

l

in m

f in

MHz

To convert frequency to wavelength in meters divide 300 by frequency in MHz.

96.5 KPEL broadcasts at 96.5 MHz so the length of the waves is 300/96.5. The waves are approximately 3 meters in length.

What property does wavelength refer to?

The distance a wave travels during

1 complete cycle.

How fast does a radio wave travel?

Speed of light

or

300,000,000 meters/second

Describe the relationship between

wavelength and frequency.

inverse

wavelength frequency

or

wavelength frequency

What is the formula for converting

frequency into wave length (in meters)?

300 / Mhz

All types of radio frequency signals are referred to by the abbreviation RF, but for convenience the entire range is spilt into sub-ranges.

3000 MHZ

Communications at VHF and UHF

are generally “line of sight” communications.

That is they travel directly from the

transmitting station to the receiving

station.

Normally used for local communication.

Direct (not via a repeater) UHF signals are

rarely heard from stations outside your

local coverage area because UHF signals

are not reflected by the ionosphere.

signals between two point are blocked by the

curvature of the Earth.

The radio horizon is somewhat farther than the

visual horizon because the earth seems less

curved to radio waves than light waves.

When using a hand-held transceiver inside a building you might want to choose to operate in a UHF band.

• UHF signals are often more effective from inside buildings than VHF signals because the shorter
• wavelengthallows them to more easily penetrate the structure of buildings.

Knife-edge propagation is the term used to describe when signals are partially refracted around solid objectsexhibiting sharp edges.

• You might be able to use this phenomenon
• to get your signal around a building in an
• urban setting.

What is the name assigned to each

of these frequency ranges?

3 – 30 MHz

30 – 300 MHZ

300 – 3000 MHz

Why are UHF frequencies usually

limited to local communications?

UHF signals are not reflected

by the ionosphere.

What do we call the distance at which

radio signals are blocked by the curvature

of the Earth?

Why is the radio horizon somewhat farther that the visual line of sight distance between two stations?

The earth seems less curved

light waves.

Why should you choose to use

frequencies in the UHF band when using

a hand-held receiver inside a building?

The shorter waves length allows them to

more easily penetrate the structure of

the building.

What do we call the phenomenon in which

signals are partially refracted (bent) around

solid objects with sharp edges?

Knife-edge propagation